You get defensive bonuses for forifying, and yes you can die if you fortify in a jungle, but it is very rare.

I use sentry on the outer rim of my empire, I will sentry one unit in each border town and maybe a few along the border or coast (naval units), they will wake when an enemy approaches. There is no defensive bonus for sentry.

The land units will only wake for enemy land units and the naval units will only wake for enemy naval units. I wish that a canon on the coast would wake for a passing enemy ship, but it does't. Other that that it works great.

Okay, that's great. One last question: If you SENTRY in a Jungle, can you die just like if you fortified? Because, I'm playing a Reverse Capture the Flag, and I just pinned an ally's princess-carrying unit. I mean trapped. But some of my units are in Jungle, and I am getting tired of skipping their turn. But I do not want to run the risk of them dying and the "ally" escaping. Will Sentry allow them to die?

I have seen my unit die from being on a fortress on a flood plain once, only once...it was on a map i was actually working on for a scenario and I was testing. On the third turn out of nowhere the unit on a fortress suddenly dies and a messages pops up saying there's disease in the flood plain. It took me by surprize really...

This is wrong. Sentried land units get the white border around the health bar signifying a fortified status, therefore they get the bonus.

I don't think that they get the bonus (at least not always) because they are awakened by the enemy and no longer have the white border during the attack. They may keep the bonus when attacked by a fast moving unit like a cavalry or tank, I will have to pay attention next time I get attacked by a fast unit.

Wow, That's amazing. I leave for one day, look at all the replies! The manual doesn't ever explain anything, so I thought I'd ask. Disease only happened to me once, but it was an Automated worker (The stupid bum). But I wasn't relying on that worker to win the game. As it is, I just kept hitting Spacebar, and they didn't die, and I won by Victory Point score. Works out good for me. My "ally" wasn't too happy, though.

Okay, that's great. One last question: If you SENTRY in a Jungle, can you die just like if you fortified? Because, I'm playing a Reverse Capture the Flag, and I just pinned an ally's princess-carrying unit. I mean trapped. But some of my units are in Jungle, and I am getting tired of skipping their turn. But I do not want to run the risk of them dying and the "ally" escaping. Will Sentry allow them to die?

Any unit in a Jungle has a risk of dying, whether or not it's Sentried, Fortified, or just standing around picking it's a**. The state it's in makes no difference, it's simply the fact that it happens to be in the Jungle at the time. So just skipping their turn isn't going to help you at all.

And it happens so rarely that you really shouldn't worry about it. Just bring in an extra unit or two for reinforcements if you're concerned about it.